An etch process may provide a method for forming a predetermined pattern on a substrate. Thus, an etch process is generally used for fabricating a precision device, such as a semiconductor device that includes fine patterns. Etch processes may be classified into dry etch processes and wet etch processes.
A wet etch is a method of selectively etching a predetermined material layer using a predetermined chemical solution. This method may be relatively productive because a plurality of semiconductor substrates can be simultaneously etched. Wet etching, however, may be less desirable when forming fine patterns due to an isotropy etch characteristic thereof. Thus, wet etching is typically used for a restrictive purpose, such as cleaning before a deposition process or removing polymer generated in a dry etch.
A dry etch may have both isotropy and anisotropy etch characteristics. Because a dry etch generally involves etching a predetermined layer using a plasma, an etched layer or bottom patterns thereunder may be etch-damaged. To reduce etch damage and form patterns having a superior quality, only a target layer is etched and etch damage with respect to the bottom patterns may be reduced. An etching end-point of an etch process, meaning a moment when the etch process should be stopped, is an important variable for accurately controlling the etch process.
In the case that the etching end-point is defined as a moment when the target layer is removed to expose a bottom structure, a method of determining the etching end-point may use an optical characteristic, such as change of index of refraction, reflexibility or luminous intensity of plasma when a bottom structure is exposed.
FIG. 1 is a flow chart that illustrates a conventional method of determining an etching end-point. Referring to FIG. 1, after loading a substrate having a predetermined material layer into an etch chamber (S1), various process conditions are set up for controlling an etch process (S2). The etch process includes an etch end condition for determining the etching end-point. Then, RF power is applied for generating an etch plasma (S3). A luminous intensity of the plasma is measured using predetermined optic equipment arranged outside of the etch chamber (S4). Until the measured luminous intensity satisfies the etch end condition, the luminous intensity is repeatedly measured per a predetermined time interval (S5). If the etch end condition is satisfied, the RF power is cut of and the etch process is stopped (S6). Then, the substrate is unloaded out of the etch chamber (S7).
However, optical characteristics measured by the plasma may be disturbed due to various causes. Thus, this disturbance may distort a determination process with respect to an etching end-point measured on the basis of the optical characteristics. A wrong etching end-point may result in a product failure because an etch process may be imperfectly finished.